Control system for a platform lift apparatus

Abstract

A platform lift apparatus moves objects vertically within a structure such as between floors of a residential or commercial structure. The platform lift apparatus further comprises a main body having a platform receiving portion and a utility portion. A drive train is substantially contained within the utility portion of the main body. The drive train comprises a rotatable shaft having plural lift drums and a motor operatively coupled to the shaft to cause selective rotation thereof. Each of the lift drums has an associated lift tether coupled thereto and wound thereon. A platform is coupled to respective ends of the lift tethers to suspend the platform from the platform receiving portion of the main body. The platform is selectively movable by operation of the drive train to travel vertically relative to the main body. The platform is substantially nested within the platform receiving portion of the main body when at an uppermost point of travel. At least one load sensor is operatively coupled to at least one of the lift tethers. The load sensor provides a load signal corresponding to load on the associated one of the lift tethers. A control circuit is operatively coupled to the motor and the at least one load sensor, wherein the control circuit controls operation of the motor responsive to the load signal. The control circuit causes the platform to travel upward by driving the motor to rotate the shaft in a first direction to wind the lift tethers onto the respective lift drums and causes the platform to travel downward by driving the motor to rotate the shaft in a second direction to unwind the lift tethers from the respective lift drums.

What is claimed is: 
     
       1. A platform lift apparatus, comprising;
 a main body having a platform receiving portion and a utility portion; 
 a drive train substantially contained within the utility portion of the main body, the drive train comprising a rotatable shaft having plural lift drums and a motor operatively coupled to the shaft to cause selective rotation thereof, each of the lift drums having an associated lift tether coupled thereto and wound thereon; 
 a platform coupled to respective ends of the lift tethers to suspend the platform from the platform receiving portion of the main body, the platform being selectively movable by operation of the drive train to travel vertically relative to the main body, the platform being substantially nested within the platform receiving portion of the main body when at an uppermost point of travel; 
 at least a first sensor operatively coupled to a first one of the lift tethers and a second sensor operatively coupled to a second one of the lift tethers, the first sensor providing a first signal corresponding to slack on the first one of the lift tethers and the second sensor providing a second signal corresponding to slack on the second one of the lift tethers; and 
 a control circuit operatively coupled to the motor and the first and second sensors, wherein the control circuit takes at least one corrective action if the first and second signals indicate slack on at least one of the first and second ones of the lift tethers; 
 wherein the control circuit causes the platform to travel upward by driving the motor to rotate the shaft in a first direction to wind the lift tethers onto the respective lift drums and causes the platform to travel downward by driving the motor to rotate the shaft in a second direction to unwind the lift tethers from the respective lift drums. 
 
     
     
       2. The platform lift apparatus of  claim 1 , wherein the control circuit is further configured to take said at least one corrective action only when said platform is traveling downward. 
     
     
       3. The platform lift apparatus of  claim 1 , further comprising at least one load sensor operatively coupled to the control circuit, the at least one load sensor providing a first electrical signal to the control circuit indicative of a load on the platform, wherein the control circuit is configured to take at least one other corrective action if said first electrical signal indicates that said load on the platform has exceeded a maximum load value. 
     
     
       4. The platform lift apparatus of  claim 3 , wherein the control circuit is further configured to take said at least one other corrective action only when said platform is traveling upward. 
     
     
       5. The platform list apparatus of  claim 1 , further comprising a position sensor coupled to the platform receiving portion of the main body, wherein said position sensor is configured to provide a position signal to the control circuit when the platform has reached an uppermost position. 
     
     
       6. The platform lift apparatus of  claim 5 , wherein said position sensor comprises a Hall-effect sensor. 
     
     
       7. The platform lift apparatus of  claim 1 , wherein the control circuit is further configured to receive a second electrical signal having a plurality of pulse widths, wherein each pulse width corresponds to a predetermined distance of vertical movement of the platform, and to count the plurality of pulse widths to determine a vertical position of the platform. 
     
     
       8. The platform lift apparatus of  claim 7 , wherein the control circuit is configured to determine the vertical position of the platform by zeroing out a counter when the platform is in an uppermost position and counting the plurality of pulse widths in the second electrical signal to determine a vertical position with respect to the uppermost position. 
     
     
       9. The platform lift apparatus of  claim 8 , wherein the control circuit is further configured to store a lowermost position during initialization, and to take at least one other action when the platform approaches the lowermost position. 
     
     
       10. A method of moving a platform in relation to a main body having a platform receiving portion and a utility portion, comprising;
 driving a motor in a first direction to wind a plurality of tethers around a plurality of drums, causing the platform to travel in an upward direction; 
 driving said motor in a second direction to unwind the plurality of tethers from the plurality of drums, causing the platform to travel in a downward direction; 
 receiving by a control circuit a first signal from a first one of a plurality of sensors at least when said platform is traveling in said downward direction, said first one of said plurality of sensors being coupled to a first one of said plurality of lift tethers, said first one of said plurality of lift tethers being used to suspend a first portion of said platform from said main body; 
 receiving by said control circuit a second signal from a second one of said plurality of sensors at least when said platform is traveling in said downward direction, said second one of said plurality of sensors being coupled to a second one of said plurality of lift tethers, said second one of said plurality of lift tethers being used to suspend a second portion of said platform from said main body; 
 receiving by said control circuit a load signal from a load sensor at least when said platform is traveling in said upward direction; 
 using by said control circuit said load signal to determine a load on said platform at least when said platform is traveling in an upward direction; 
 using by said control circuit said first and second signals to determine, respectively, whether there is slack in said first and second ones of said plurality of tethers when said platform is traveling in a downward direction; 
 performing at least one corrective action if said load is greater than a maximum load value; and 
 performing at least one other corrective action if it is determined that there is slack in at least one of said first and second ones of said plurality of lift tethers. 
 
     
     
       11. The method of  claim 10 , wherein said step of performing at least one corrective action if said load is greater than a maximum load value comprises at least one of stopping said motor from being driven in said first direction and driving said motor in said second direction. 
     
     
       12. The method of  claim 10 , wherein said step of performing at least one other corrective action if it is determined that there is slack in at least one of said first and second ones of said plurality of lift tethers further comprises at least one of stopping said motor from being driven in said second direction and driving said motor in said first direction. 
     
     
       13. The method of  claim 10 , further comprising the step of receiving by said control circuit a position signal from a position sensor to determine when said platform has reached an uppermost position. 
     
     
       14. The method of  claim 10 , further comprising the step of receiving by said control circuit a signal indicative of vertical movement and using said signal to determine a vertical position of said platform. 
     
     
       15. The method of  claim 14 , further comprising the steps of using a position signal to identify an uppermost position of said platform, storing a lowermost position of said platform in memory, using said signal indicative of vertical movement to identify a position of said platform with respect to said uppermost position, and performing at least one action immediately before said position of said platform reaches said lowermost position. 
     
     
       16. The method of  claim 14 , wherein said step of performing at least one action immediately before said position of said platform reaches said lowermost position comprises slowing said motor as said platform approaches said lowermost position. 
     
     
       17. A platform lift apparatus, comprising;
 a main body having at least a platform receiving portion; 
 at least one motor configured to move a platform vertically with respect to said main body by winding and unwinding a plurality of lift tethers; 
 said platform coupled to respective ends of the plurality of lift tethers to suspend said platform from said platform receiving portion of said main body; 
 at least a first sensor operatively coupled to a first one of the plurality of lift tethers and a second sensor operatively coupled to a second one of the plurality of lift tethers, the first sensor providing a first signal corresponding to slack on the first one of the plurality of lift tethers and the second sensor providing a second signal corresponding to slack on the second one of the plurality of lift tethers; and 
 a control circuit operatively coupled to the motor and the first and second sensors, wherein the control circuit takes at least one corrective action if (i) the first and second signals indicate slack on at least one of the first and second ones of the plurality of lift tethers and (ii) said platform is traveling in a downward direction; 
 wherein said control circuit causes said platform to travel upward by driving said at least one motor to rotate in a first direction to wind said plurality of lift tethers onto respective receiving devices and causes said platform to travel downward by driving said at least one motor to rotate in a second direction to unwind said plurality of lift tethers from said respective receiving devices. 
 
     
     
       18. The platform lift apparatus of  claim 17 , further comprising at least one load sensor operatively coupled to the control circuit, the at least one load sensor providing an electrical signal to the control circuit indicative of a load on the platform, wherein the control circuit is configured to take at least one other corrective action if (i) said electrical signal indicates that said load has exceeded a maximum load, and (ii) said platform is traveling upward. 
     
     
       19. The platform lift apparatus of  claim 17 , further comprising a position sensor coupled to the platform receiving portion of the main body, wherein said position sensor is configured to provide a position signal to the control circuit when the platform has reached an uppermost position. 
     
     
       20. The platform lift apparatus of  claim 19 , further comprising a movement sensor configured to provide a movement signal to the control circuit, the control circuit using said position signal, said movement signal, and a predetermined lowermost position to take at least one action when said platform approaches said lowermost position.